Mycoplasma bovis: Diagnosis and prevention

Immunohistochemistry of a lung lesion showing Mycoplasma reactivity in the center of the abscess, field case.

Photo credit: Ricardo Rosenbusch, DVM, PhD

Editor’s note: Last in a Mycoplasma bovis roundtable series.

Eye-balling a sick feedlot animal with pneumonia and saying for sure that it has a Mycoplasma bovis disease is a tenuous diagnosis at best. It may very well have an M. bovis infection, but most likely it also has bovine viral diarrhea virus (BVDV) or other pathogens that are at work.

Diagnosing M. bovisDiagnosing an M. bovis infection isn’t easy. “To me, the biggest challenge to the producer and the veterinarian is detecting early symptoms of Mycoplasma bovis,” says Ricardo Rosenbusch, DVM, PhD, Iowa State University. “With other diseases, you get early symptoms, and then you can have relatively early intervention. With Mycoplasma bovis, you get a call because someone has crippled calves. Those calves have had a pneumonia for 15 days and an arthritis for three or four days. They’ve probably been treated, and you’re coming in for the second treatment. The chances of success are going to be relatively low because of late intervention.”

Rosenbusch has been searching for early signs that might indicate an M. bovis problem. “Is there a cluster of early signs you can look for? Veterinarians who deal with veal operations look for conjunctivitis as a reliable early sign. They look at calves coming in at 7 or 8 days of age. If they break with conjunctivitis, they start worrying about Mycoplasma bovis. They put them in an early almost-metaphylactic treatment.”

On the other hand, Rosenbusch notes, the feedlot and stocker operators seem to rely on a moist cough as a symptom. “They don’t see enough conjunctivitis as a symptom because they have problems with flies and most calves already have conjunctivitis. They’ve learned to associate a moist cough presentation at a week after arrival with Mycoplasma bovis. I wish we had better science.”

Rosenbusch notes that in a study where calves were infected with a known strain of Mycoplasma bovis and transported to a feedlot, there was a major outbreak in the feedlot. Every dead animal was necropsied. “We had a significant mortality of 7 percent. We observed every animal, and we knew exactly on which day the infection was started. Every strain of Mycoplasma bovis that came out of that outbreak had the same fingerprint as the one we put in.”

However, the cowboys could not find the Mycoplasma bovis animals. “They were correctly pulling out the Mannheimia hemolytica cattle and they were being treated, but the M. bovis animals were not pulled,” Rosenbusch says. “Febrile responses reached 103° but were never high enough to cause a severe enough depression for the cowboy to pull the animal.”

Within this consolidated lung, there are many raised, white-yellow, sharply demarcated foci of caseous necrosis. Cheesy exudate may be expressed from a cross-section of lung. These foci of necrosis are often 2-10mm in diameter but occasionally coalesce to form large areas of necrosis.

Photo credit: Dan Grooms, DVM, PhD

Necropsies What do Mycoplasma bovis lesions look like? Rosenbusch explains that there are two types of Mycoplasma bovis strains. Fifty percent of the strains coming from the field will produce abscesses and 50 percent will not. With abscessing strains, the presentation in the lung will be a coagulative necrosis lesion that can be up to 5mm in diameter, never much larger than that. Histologically, the center has formed around a bronchus that has accumulated a lot of neutrophils. The epithelium is still normal. That whole area of accumulation of neutrophils expands and is surrounded by a band of mononuclear cells, monocytes and lymphocytes. There’s very little evidence of a fibrotic capsule; often there’s no capsule whatsoever. “It’s not truly an abscess like you would see with a Pasteurella multocida abscess.”

The lesions don’t grow beyond that even if the animals have been clinically affected for 40 to 50 days. Lesions tend to be cranial in distribution but can be in the diaphragmatic lobes also. Wherever there are small localized lesions, the surface of the lung will be elevated. “It has goose bumps all over it, which is something you do not see in M. hemolytica,” notes Rosenbusch. As you cut, you see relatively dry, white caseous lesions. “You almost always see that the septums of the lung are enlarged, and the histopathology to that is thrombosis of the lymphoid system of the lung. The septums are tremendously enlarged on histological examination. When you look at the lung, you can see the divisions between the lobes much more than in a normal lung or an M. hemolytica or a P. multocida lung.”

The lung from a Mycoplasma mycoides infection shows a yellow, stringy, well-demarcated limit to the lung lobules and a deep meat-red color of the tissue in between. “That’s very similar to what Mycoplasma bovis looks like,” says Rosenbusch.

These classic lesions are what Dan Grooms, DVM, PhD, Michigan State University, sees as well. “Maybe we misdiagnosed this, but at times, I’ll see that classic small abscess throughout the cranial-ventral distribution, and in the midst of that, we’ll see what looks like some have been coalescing together to form a bigger area of necrosis. More commonly, we see the miliary lesions throughout the lung.”

“When we first started looking at these lesions, we thought about tuberculosis,” says Rosenbusch. “Miliary is an OK term, but in abscesses, it’s not a caseous type of lesion. What’s missing is the fibrotic component. You don’t see bundles of fibroblasts and a lot of collagen.”

Mycoplasma bovis lesions are clearly different compared to M. dispar, says Rosenbusch. “I don’t think you would even need immunohistochemistry. Pathologists who have seen M. dispar or even M. hyopneumoniae in a pig lung, and then who have looked at an M. bovis lung, clearly know it’s a totally different species. Also, many pathologists who started using immunohistochemistry have dropped it to lower the cost to the consumer. They’re now doing diagnosis on histopathology only because their eyes are already trained. They can do a very good job and can be over 90 percent accurate with histopathology alone.”

Severe synovitis and arthritis of the stifle joint extending distally into the tendon sheath of the peroneus tertius.

Photo credit: Dan Grooms, DVM, PhD

Bob Glock, DVM, PhD, Arizona Veterinary Diagnostic Laboratory, adds that a pet peeve as a diagnostician is when people who are looking at almost any lung abscess automatically call it Mycoplasma. “To me, these are not typical abscesses because they tend not to develop a capsule of fibrosis. They are really areas of coagulative necrosis. I see a lot of abscessed lungs that I can explain with Arcanobacterium pyogenes. I think we’ve gone overboard in looking at an abscess and declaring it a Mycoplasma.”

Tom Noffsinger, DVM, Twin Forks Clinic, Benkelman, Neb., believes more slaughter audits need to be done to help get a handle on Mycoplasma lesions. “What my treatment crews are telling me is that if we have 1,000 head of calves come through the hospital, the incidence of Mycoplasma lesions at slaughter in the calves that responded to a very short, intense treatment is low. The incidence of Mycoplasma lesions in the lungs of re-treat pens is much higher. We’re finding that those lesions were present on arrival or shortly after.”

Rosenbusch agrees. “The swine industry has learned that unless you do pre-slaughter checks, you will not get a true picture of Mycoplasma and pneumonia. I think what’s going to happen in the cattle industry is that we’re going to have to bite the bullet and necropsy a fraction of our animals at 15 to 30 days after arrival until we learn what we’re doing. It’s a big expense,” he concedes, but “we will be blind until that happens.”

Samples for diagnosisAs far as clinical diagnostics, Noffsinger has found Mycoplasma mainly by the use of PCR on lung tissues, in conjunction with aerobic and anaerobic bacterial cultures and looking for viruses, such as BVDV, in tissues. He usually submits lymph nodes and lungs when diagnosing respiratory disease.

Because of middle-ear infections in younger and veal calves, Alvin Baumwart, DVM, Highland Veterinary Clinic, Arapaho, Okla., typically sends the soupy ear or joint fluid to the lab for a diagnosis and believes the gold standard for diagnosis is culture. “I want it demonstrated in the lab before I will say it’s M. bovis,” he says.

Grooms adds that pathologist Ted Clark, DVM, Dipl. ACVP, from the Western College of Veterinary Medicine, recommends sending in synovial tissue, as well as joint fluid. “He thinks we get better isolation results,” says Grooms. “So we turn in not only fluid but also a piece of the synovium to help increase our yield.”

Rosenbusch prefers using the immunohistochemistry test because it gives a pathology link to a high-level presence of Mycoplasma in the lesions. “We won’t get an immunohistochemistry-positive signal unless we have 107 or 108 Mycoplasma accumulating in one location. That’s a lot of Mycoplasma in one spot.”

He says most PCRs can detect 103 or 104 organisms from a sample. “What goes into a PCR reaction is less than a tenth of a milliliter, so even if you send 10mL of ear exudate or a big chunk of lung, they’re going to sample a very small amount. So Mycoplasma has got to be there at the site of sampling or you miss out. Even with immunohistochemistry, you can section only a piece big enough to put on a 2-in. by 1-in. slide. If we sample the wrong part of the lung, we’re not going to get the immunohistochemistry signal. I think there are gross lesions that are classical enough that they can guide a pathologist or a veterinarian in the field.”

Richard Sommers, DVM, believes in necropsying as many dead animals as possible.

Richard Sommers, DVM, Silver Lake Veterinary Clinic, Inc., Silver Lake, Ind., notes that some clients don’t want to spend money on diagnostics anymore. “They just assume Mycoplasma is going to be there, and they feel they’d be better off spending the money on vaccine.”

Rosenbusch says that may be true to some extent. “There can be a resistance to going to the diagnostic lab as prices go up. Immunohistochemistry now is in the range of $50. A PCR is probably in the range of $30 for an individual animal. You talk about ideal diagnostic situations, but the real world clashes with the economics of diagnostics more and more.”

Baumwart agrees that economic realities play a role in necropsies. “The cost of animals is up, and the cost of necropsies is up. Also, the dead-animal fees have escalated. If we necropsy an animal, the renderer may or may not pick it up. We’ve reached a new era in how we handle our deads. I don’t know how BSE is going to affect the dead-animal service. That does have an indirect effect on necropsies. People are not bringing us their dead animals as they used to. They want answers, but they want telephone answers.”

“This is a touchy subject,” adds Rosenbusch. “Mycoplasma bovis has mortality. We’re going to be dealing with necropsy and with carcass disposal.”

But for Noffsinger, necropsies and diagnostics are important, at least on the feedlot level. “In the operations where we see the best progress, every animal that dies is posted. The triangle between teaching diagnostics and observation and pathology is very important for management, for veterinary staff and for lay people.”

Sommers also believes in necropsying as many dead animals as he can. “The point I emphasize to my clients is that a dead animal is an opportunity for us to learn and to not make the same mistake again. It’s not a hard sell in my practice. We have only one renderer left in our area and may have to go to composting. I’m as concerned as everyone about the BSE/composting issue. But there is a wealth of information within that dead animal.”

Prevention – stockers and feedersSommers believes in having a plan for immunizing stocker cattle. He has an injection-site map for every vaccine so he knows what is put where and when. He never puts viral and bacterial vaccines on the same site with the exception of a core antigen vaccine that will co-exist with a viral vaccine. “Whatever side we choose for the Mycoplasma the first time, we put it on the opposite side two weeks later. We’ve been doing this for 18 months on one particular stocker operation with much success.” He says the stockers get TSV-2 and Mycoplasma 12 to 24 hours after arrival, plus a dose of 5-way MLV vaccine, a core antigen vaccine and a dose of modified-live Pasteurella vaccine. “It doesn’t make any difference if they’re four-weights or seven-weights; they all get the same thing.”

Sommers adds that there is also a Hemophilus problem on this operation. “We always give the Hemophilus vaccination by itself and the modified-live Pasteurella separate. This client changes needles on every 16 to 18 animals. A dirty needle never enters the vaccine bottle.”

For stockers purchased through sale-barn operations, Baumwart recommends Mycoplasma bovis and a double dose of modified-live respiratory vaccine. “When I saw the poly-arthritis problem solved because of the Mycoplasma vaccine, I felt more strongly about recommending the vaccine to stocker operators.” For northern ranch cattle, however, he’s not recommending Mycoplasma vaccination.

Sommers believes stress at vaccination has a lot to do with vaccine performance. “Any animal or human’s immune system can be overcome by too much stress. When I get an animal that’s not stressed, that animal responds to the vaccine. Then it’s up to choosing which vaccine to use. I don’t think you can use multiple mixtures of vaccines. Combining viral vaccines in the same syringe with bacterial vaccines is wrong, because I don’t think that animal’s immune system is capable of mounting a proper immune response to these types of vaccinations. So you choose the vaccines that you think are the most important and give them separately.”

He adds that if an animal has had a modified-live vaccine while still on the cow or two weeks prior to shipment, then it will probably respond better to a Mycoplasma bovis vaccine. “You may give it another modified-live vaccine on arrival with little stress because it’s already got an immune response. It can concentrate on Pasteurella and Mycoplasma, for instance.”

Sommers thinks that getting stocker operators to vaccinate for M. bovis will be a hard sell. “It’s difficult to get them to vaccinate even for the viruses. If I had to rank them in order, I’d vaccinate them for the viruses, and second, I’d vaccinate with a good Pasteurella vaccine. If we can’t get these guys to vaccinate the cow or their calves, how are we going to get them to give Mycoplasma?”

Rosenbusch adds that in the 2002 Kansas Mycoplasma stocker survey, about 14 percent of respondents were using some type of killed Mycoplasma bovis bacterin in stockers (www.beefstockerusa.org). “That’s a significant amount of use for that industry in Kansas.”

Is Mycoplasma bovis vaccination at the feedlot too late for any response? “Our biggest dilemma is that when they get off the truck at the feedyard, it’s too late to start the process of immunization, and it’s a huge challenge for us to overcome,” states Noffsinger. “The use of Mycoplasma vaccine on arrival in high-risk cattle at the feedyard in my locale has not changed morbidity or mortality or arthritis symptoms. I don’t know if our management is so poor that it overrides the vaccine.”

Noffsinger is interested in whether the use of these products can help. “If we have a load of calves coming in from multiple origins and 30 percent already have changes in their lungs, will a couple of doses of these products help the other 70 percent?”

“We’re looking at more than just immunity to Mycoplasma,” adds Baumwart. “We’re also looking at viruses and Pasteurellas.”

Sommers indicates that his clients’ feedlot animals that have been vaccinated for Mycoplasma bovis also have very few middle-ear infections, and he’s seen a decrease in arthritis. These animals are vaccinated upon arrival and then two weeks later in the opposite side of the neck. “I think there’s an opportunity, by using the vaccine, to not have to concern ourselves with treatment. I don’t think treatment is going to be highly successful anyway. Everybody wants a cure-all, and it’s not out there. The best treatment is prevention.”

Grooms adds that a Michigan feedlot veterinarian has tried multiple times to use Mycoplasma vaccines at the feedlot level but has not had much luck in reducing morbidity or mortality. “I’ve had two opportunities where I’ve used Mycoplasma vaccines and we have had luck, but in both instances, we also made major management changes,” says Grooms. “The change in management may have made as big a difference as the vaccine, but I can’t convince them not to use the vaccine because things are better. To me, the jury is out on these vaccines. I do believe we can probably make as much of a difference through management changes.”

Prevention – cow-calfVeterinarians have differing opinions on vaccinating calves on cows. Baumwart recommends a double dose of killed viral vaccine on calf operations when the calves are going back on the cows. “People who are willing to follow any vaccination program are going to buy higher-priced and better-quality cattle. The people who need more vaccine and better management are going to continue to cut corners.”

Baumwart has seen pneumonia in his home-grown stockers, but no polyarthritis that he has diagnosed as Mycoplasma. “I still recommend modified-live vaccine if the calves are not going back to the cows,” he says.

Sommers has been able to trace back and found that calves receiving two modified-live vaccinations while still on the cow were much superior to animals that received killed vaccines. “In the mama-cow herd, if vaccinated well enough that you can give modified-live to the calves, those calves are the cream of the crop,” he says. “That type of cowman is also most likely to give the Mycoplasma vaccine because he is a top-flight operator.”

“It’s important for us to get a nice modified-live vaccine in that calf as soon as we can, whether it be branding or pre-weaning,” adds Noffsinger. “The industry is learning. I don’t know where we got this 205-day weaning date. That’s obviously the time that well-bred animals are changing gears from passive immunity.”

Noffsinger’s vaccination program is based on modified-live viral products given multiple times. “I think getting vaccines into the calf is the only chance we have to change the production system. We don’t know about the efficacy of the vaccines, but if there’s a place for the use of them, the calf level is the place.”

Grooms agrees. “If a Mycoplasma vaccine has a place, that’s probably where it needs to be used. But, is the Mycoplasma vaccination necessary if we vaccinate them for the other things – the viruses that may be the predisposing problem – and then we manage them correctly? That’s where we need research. If calves are preconditioned correctly before they go into the backgrounding operation, we’re covering them during that critical high-risk period.”

It’s not just about vaccination, adds Baumwart. “I don’t think we would disagree that if the building blocks of nutrition and immunology are not there, we’re fooling ourselves. We need to get those animals up to speed as far as immunology, or diseases like Mycoplasma bovis and others will come in and haunt us.”

Once again, prevention comes around to economics. “The only way you’re going to make part of this work is for somebody at the feedlot end to pay a good premium to have calves vaccinated,” says Sommers. “They have to pay premium enough to give the cow-calf guy the incentive to get it done right.”

Baumwart believes the industry is on the right road. “Diagnostics are increasing. The knowledge base is increasing, not only to veterinarians but to lay people, our technicians and to our cattle owners. I think we’re challenged, and I don’t think it’s going to stop here. We need to know more about the problem and potential solutions.”

This information is from a Bovine Veterinarian Mycoplasma bovis roundtable sponsored by Boehringer Ingelheim and moderated by Bob Glock, DVM, PhD.

Economics of mycoplasma infections

Economic data surrounding Mycoplasma infections is difficult to come by, but we do know that treating cattle for Mycoplasma in the feedlot is very costly. “The presence of this organism in a group of calves can have almost zero effect on total morbidity, but can double the treatment cost,” says Tom Noffsinger, DVM. “Your cost can go from $21 to $42. And that doesn’t include labor, chute fees, the extra effort in the system.”

“My limited experience would indicate the feedlots or even stockers would have a 30 percent pull rate under non-Mycoplasma bovis conditions,” adds Ricardo Rosenbusch, DVM, PhD. “They say 30 percent of arrivals would have to have some kind of medication. When Mycoplasma bovis is involved, that number jumps up to close to 80 percent.”

It’s even more difficult to assess costs in the cow-calf industry. “The cow-calf sector is a big black hole,” says Rosenbusch. “We don’t know the incidence. We don’t know how many are positive for Mycoplasma bovis, but arthritis and middle-ear infection seem to be a much lower frequency event.”

That’s not to say that arthritis and otitis in cow-calf operations isn’t costly. “You treat them for two weeks and send them home still limping and head-tilted, and you hope everything is all right,” says Alvin Baumwart, DVM. “In the past, if you knew they were going to have multiple joints, you’d tell them they’re better off not spending the money. Economically, it’s crushing, but the breath of fresh air is that there might be some alternatives out there.”

Baumwart says drug costs could be as high as $15 per day for two weeks, plus hospitalization if calves are brought in, and “that’s conservative for hospital charges.”

Dan Grooms, DVM, PhD, notes a producer he worked with who lost 58 out of 144 calves four weeks into the feeding period. Necropsies isolated Mycoplasma bovis in 29 of 33 calves, and BVDV was isolated in those 33, as well. Grooms believes Mycoplasma and BVDV were working synergistically. “That’s obviously a significant eco-nomic hit to this producer,” he says.

Mycoplasma bovis diagnosis

A lot of cattle carry and shed M. bovis; therefore, it is important to find M. bovis in affected tissue from an animal with a compatible clinical history, says Bob Glock, DVM, PhD.

When submitting samples to a diagnostic lab for M. bovis, Glock recommends sending:

Postmortem samples Affected lung Tendon sheathAffected tissues should be submitted in formalin along with any other lesions seen at necropsy. Samples should be refrigerated but not frozen if held less than three days.

There are a variety of test choices available. Glock suggests talking to the lab you use to determine what they offer and what they prefer. Advantages and disadvantages of different tests are:

IHC. Immunohistochemistry is a very reliable test to define if the animal is affected by M. bovis.

PCR. Very sensitive; preservation of specimens is less critical. This test should be used by a lab that has the ability to identify M. bovis.

Culture. Preservation of specimens is critical; samples should arrive refrigerated in less than two to three days.